An existing device includes a housing with an opening therein which is closed by a lid, the lid including a frame hermetically sealed to a window transmissive to radiation in a waveband of interest. The device can be used in a television or a projector to form images, which are typically projected onto some type of screen so that they can be viewed by a person. The device includes within the housing a digital micromirror device (DMD) of a known type. A beam of radiation enters the housing through the window in the lid, is processed by the digital micromirror device to form a plurality of sub-beams that represent an image, at least some of the sub-beams then exiting the housing through the window in order to facilitate the generation of the image which is projected onto the screen.
This existing lid is made by forming a metal frame which has an opening through it, placing a piece of glass in the opening through the frame, and heating the frame and glass until the peripheral edges of the glass become fused to the edges of the opening in the frame. While this existing lid and the process of making it have in generally adequate for their intended purposes, they have not been satisfactory in all respects.
In this regard, since the glass is fused to the frame by heating the glass to a temperature in the region of its melting point, various imperfections can be introduced into the glass, and these imperfections need to be subsequently polished out of the glass. A further consideration is that, in the existing type of device discussed above, a gas is provided within the housing in order to facilitate lubrication of the tiny movable mirrors of the DMD, but this gas also tends to be somewhat corrosive to other materials such as the metal of the frame, and thus the portions of the lid which are exposed to the gas must be resistant to its corrosive properties.
A further consideration is that, since the window is heated to temperatures that may produce imperfections which have to be subsequently polished out, certain steps in the fabrication process are carried out on a lid-by-lid basis after the window of each lid has been fused to the frame, and after any resulting imperfections have been polished out. For example, in some applications it is desirable to have an anti-reflective coating on one or both sides of the window, and each such coating is applied on a lid-by-lid basis after the window has been fused to the frame and after any resulting imperfections in the window have been polished out.